The invention relates to a device for controlling an electric motor, especially an electric motor in motor vehicles.
Such a device is known, for example, in connection with a setting element, which can be adjusted by way of the electric motor, for setting a variable valve lift in BMW's Valvetronic® internal combustion engines.
The operating principle of such Valvetronic® internal combustion engines is explained briefly by use of the drawing in FIG. 2. A cam shaft 1, for example the cam shaft assigned to the intake valves, does not directly actuate the valves 2, but rather actuates the valves by way of an intermediate lever 4. An electric motor (for example, the electric motor M in FIG. 1), which is not depicted in FIG. 2, drives a setting element 3 in the form of an eccentric shaft, which acts on the intermediate lever 4 and changes thereby the valve lift of the valves 2. The electric motor is controlled by an electronic controller, e.g., the electronic internal combustion engine controller. At the startup of the controller, a readjustment of the electric motor usually takes place as a function of the deviation of the actual setting from the nominal setting of the setting element 3. The actual setting of the setting element 3 is detected by use of a sensor in the controller.
The object of the invention is to improve upon such a device with respect to the control of the electric motor, when a readjustment is not possible.
The invention meets this and other needs, by use a device for controlling an electric motor, especially in motor vehicles, for setting a setting element, moved by the electric motor, as a function of the deviation of an actual setting from a nominal setting of the setting element by way of a controller, which contains a microprocessor that carries out a hardware initialization routine at least in one step and a software initialization routine optionally in a second step, once the controller has been switched on, before the actual setting of the setting element can be determined in the controller. The microprocessor is constructed such that it short-circuits the electric motor independently of the actual setting of the setting element, immediately after the hardware initialization routine, by generating a defined switching state of its outputs, associated with the control of the electric motor. An advantageous further development of the invention are described and claimed herein.
The invention is based on the recognition that a readjustment is not possible, when the controller has not been put totally into operation, e.g., at reset, or not yet, e.g., shortly after reset or at the start of the switching-on operation during the startup procedure of the internal combustion engine. The reason for this lies in the hardware and software initialization routines that are usually carried out when an intelligent controller, which contains a microprocessor and a program, is put into operation. The full operability of such a controller—said operability usually being a condition for implementing electronic control operations—is not guaranteed until after completion of these initialization routines.
Therefore, according to the invention, the setting element (if it itself is an electric motor) and/or the electric motor, which controls the setting element and is used for slowing down the setting element, is short-circuited—at least as long as a readjustment operation with respect to a specific setting element is not possible, because, for example its actual setting cannot be determined yet. This short-circuiting is done as soon as possible after the controller has been switched on.
The subject of the invention defines the first initialization routine immediately upon switching on the controller, after which the microprocessor may enable its outputs, as the hardware initialization routine. Therefore, the completion of the hardware initialization phase is the earliest time at which at least one control operation of an actuator, such as the electric motor, may be carried out. At this time the electric motor is short-circuited, according to the invention, for the purpose of slowing it down by suitably enabling the outputs of the microprocessor that are necessary for this process. The short-circuiting of the electric motor is preferably the first action that is carried out by the microprocessor in order to prevent an uncontrolled actuation of the electric motor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.